As the photographic film art advances different types of film are introduced. These different types of film often have different widths. Additionally, the films are of much improved resolution requiring hold-down devices that hold the film down flat with great dimensional accuracy and with no distortion. These advances have created the need for new devices to handle the film more accurately and with greater ease.
Typically, hold-down devices comprise tables for accommodating a fixed size of photographic film that are used in conjunction with an optical imaging device to view or analyze the film. Hold-down devices have included edge clamps which clamp onto the edge of the photographic film. This is undesirable because it results in a loss of image at the edge. Weights have also been used to hold down the photographic film. But weights have resulted in distortion of the table or platen resulting in a loss of accuacy as well as a loss of that portion of the image under the weights. Because of the very high resolutions required in some applications these distortions are unacceptable.
Hold-down devices have also been used which have a vacuum slit along the peripheral edges of a platen to hold down the edges of a particular size of film. However, the peripheral edge vacuum film hold-down devices cannot adapt to various widths of film. Therefore, a different platen is needed for each different size of film.
Many of these devices do not provide for a uniform hold-down pressure over the entire surface of the photographic film. This results in the liklihood of unacceptable distortion due to the film not being held perfectly flat.
Another type of photographic film hold-down device that has been used is a table or platen having pinholes predetermindly spaced therein to supply a vacuum which holds down the film. The pinhole vacuum hold-down device is not applicable to a device requiring a transparent table or platen.
While all of these photographic film hold-down devices have adequately held down film for various applications none of them can adequately address the problem of automatically adapting to different widths of film while keeping the film flat and very precisely positioned within tight tolerances, and without loss of images near the edges of the film.